1. Field of the Invention
The present invention relates to a structure for interconnection between semiconductor chips, between MCMs (multichip modules) or between an MCM and a semiconductor chip packaged on a printed board, or more in particular to a structure for mounting a semiconductor or an MCM accurately at a predetermined position on the board in order to obtain a superior optical coupling between the parts and an optical waveguide for optical communication between the parts on the printed board.
2. Description of the Related Art
With an increase in signal transmission speed and an increased density of wirings and parts, the technique of electrically interconnecting parts on a printed board has posed the problem that an increased wiring resistance, due to the skin effect, appears and that crosstalk between wiring is caused during communication between the parts. The increased wiring resistance leads to an increased heat generation and the crosstalk disturbs the signal waveform causing a malfunction. In this way, electrical methods of interconnection have almost come to a limit of speed and density.
A method for solving the problem mentioned above is to secure an optical connection in which the parts packaged on a printed board communicate with each other using an optical signal.
FIG. 18 shows a structure for optical communication between the parts packaged on a printed board.
In FIG. 18a, 101 designates a printed board, 102 waveguides, 103 and 104 IC packages, 105 electrical circuit chips, 106 optical device arrays, 108 leads and 109 ball bumps.
The IC packages 103 and 104 each have built therein the electrical circuit chip 105 and the optical device array which is an assembly of light-emitting elements and photo-detectors. This packages is also called an OEIC package in view of the fact that electrical circuits and optical devices are integrated. Also, the optical device array 106 is electrically connected with the electrical circuit chips through the ball bumps 109. The printed board 101 has buried therein a plurality of the waveguides 102 corresponding to the elements of the optical device array for transmitting an optical signal exchanged between the parts arranged on the printed board. The leads 108 receive power from a power supply unit not shown and supply it to the electrical circuit chips 105 and the optical devices 106 in the IC packages.
FIG. 18b is a bottom view of the IC packages 103 and 104. In FIG. 18b, 112 designates radiation holes of the light-emitting elements of the optical device array or incidence holes of the photo-detectors.
The diameter of a radiation hole 112 and an incidence hole 112 is about 20 xcexcm and the holes are arranged at intervals of about 100xcexc.
FIG. 18c is a top plan view of the printed board 101. In FIG. 18c, 121 designates pads and 122 openings of waveguides.
The pads 121 are supplied with power from a power supply unit not shown and connected width a power terminal or a GND terminal 108. The openings 122 of the waveguides are placed in opposed relation to the radiation holes or the incidence holes 112. The diameter of each opening 122 is about 50 xcexcm to 90 xcexcm, and the openings are arranged at intervals of about 100 micrometers.
With reference to FIGS. 18a to 18c, the optical communication between the IC package 103 and the IC package 104 will be explained. In this case, an optical signal is assumed to be sent from the IC package 103 to the IC package 104.
The IC packages 103 and 104 are supplied with power from a power supply unit not shown through the pads 121 and the leads 108.
The electrical circuit chip 105 of the package 103 outputs a signal (electrical signal) to the electrical circuit chip 105 of the package 103. The signal output from the electrical circuit chip 105 is converted into an optical signal in the light-emitting elements of the optical device array 106, and radiated toward the openings 122 of the waveguide from the radiation holes 112. The optical signal passes into the waveguides 102 from the openings 122, proceeds in the waveguides 102 and is output toward the incidence holes 112 of the IC package 104 from the openings 122 of the IC package 104. The optical signal received by the IC package 104 is converted into an electrical signal by the photo-detectors.in the optical device array 106 and output to the electrical circuit chip 105.
The use of the above-mentioned technique of interconnection permits exchange of an optical signal between parts and eliminates the need of electrical connection, obviates the problems of increased wiring resistance and crosstalk, and thus can increase the signal transmission speed and the density of parts and wiring.
As shown in FIGS. 18b and 18c, however, the openings 122 and the radiation and incidence holes 112 of the waveguides are so small that the registration between the waveguides and the optical devices requires a highly accurate optical coupling technique. The registration error must be controlled to not more than 10 xcexcm. Also, the LD (laser diode) used as the light-emitting element and the PD (photo-diode) used as the photo-detector have a low heat resistance, and are liable to be broken by a thermal stress when soldered for packaging.
The object of the present invention is intended, taking the above-mentioned problem into consideration, to provide a highly accurate technique for optical coupling between parts and a packaging technique exerting only a small stress on the optical devices in such an optical coupling.
In order to solve the above-mentioned problem, according to the invention, a socket for receiving a semiconductor part including photoelectric elements is arranged on a printed board. According to a first aspect of the present invention, the position of packaging a semiconductor part on the printed board is defined, and therefore the accuracy of registry between the optical transmission path on the printed board and the optical device of the semiconductor part is improved.
Preferably, the socket includes a power terminal for supplying a source voltage to the photoelectric elements of the semiconductor part. Preferably, the change in the terminal shape of the part can be met simply by redesigning the socket, and therefore the multipurpose applicability of the printed board is maintained.
Preferably, the semiconductor part inserted into the socket and the insertion holes of the socket for the semiconductor part are placed in spaced relation to each other. As a result, the correct position of arrangement of the semiconductor part is held within a predefined range, resulting in an improved working efficiency.
Preferably, the semiconductor part packaged on the printed board includes light-emitting elements for transmitting an optical signal and photo-detectors for receiving the optical signal emitted by the light-emitting elements. The semiconductor part emits an optical signal, and receives the optical signal by itself through the optical device arranged on the printed board. The degree of optical coupling between the printed board and the semiconductor part can be determined.
Preferably, the optical device arranged on the printed board is specified as an optical transmission path. Unless both the light-emitting elements and the photo-detectors of the semiconductor part are optically coupled to the openings of the optical transmission path, the semiconductor elements cannot receive the optical signal emitted by themselves. In other words, the structure is such that the registration between two points of a semiconductor part and two points of the printed board can be achieved at the same time by receiving the optical signal.
Preferably, an optical device for optical communication with the photoelectric elements arranged on the printed board is included in the semiconductor part packaged on the printed board. The right packaging position of the semiconductor part on the printed board can be checked by optical communication between the printed board and the semiconductor part and verifying the degree of optical coupling. Preferably, the semiconductor part includes a plurality of optical devices corresponding to the photoelectric elements, respectively, arranged on the printed board. A plurality of points of the semiconductor part and a plurality of points of the printed board can be registered with each other, and the semiconductor part can be defined to a single orientation.
Preferably, the semiconductor part includes an electrical circuit chip operated by the power supplied from an external source and photoelectric elements for exchanging the optical signal and the electrical signal between the electrical circuit chip and the optical device on the printed board. The optical communication is possible between a plurality of semiconductor parts packaged on the printed board. Therefore, the electrical wiring is eliminated, and the increased heat generation and crosstalk which otherwise might occur, due to the increased transmission rate and the increased density of the transmission path, can be suppressed.
Preferably, there is provided a printed board on which a semiconductor part including photoelectric elements is packaged, and an optical transmission path is arranged for returning the optical signal, emitted by the semiconductor part, to the same semiconductor part. The optical signal output from the semiconductor element is returned to the particular optical signal. Unless the photoelectric elements of the semiconductor part are optically coupled to both the inlet and outlet of the optical transmission path, however, the optical transmission path can neither receive nor output the optical signal. In other words, the structure is such that the registration between two points of the semiconductor part and two points of the printed board can be accomplished at the same time by the receipt of the optical signal.
Preferably, photoelectric elements are arranged on a printed board for performing optical communication with an optical device included in a semiconductor part mounted on the printed board. According to an aspect of the present invention, optical communication is conducted between the printed board and the semiconductor part, and the degree of optical coupling is verified, so that the correct packaging position of the semiconductor part on the printed board can be found.
Preferably, a plurality of photoelectric elements corresponding to the respective optical devices of the semiconductor part are arranged on the printed board. A plurality of points on the semiconductor parts can be registered with a plurality of points on the printed board, and the position of the semiconductor part is defined by a single orientation.
Preferably, there is provided a printed board on which a semiconductor part including light-emitting elements, photo-detectors and photoelectric elements is packaged. Further, an optical transmission path with an end thereof optically coupled to the light-emitting elements of the semiconductor part and with the other end thereof optically coupled to the photo-detectors is arranged on the printed board. The board has such a structure that the optical signal transmitted from the semiconductor part is returned to the semiconductor part through the optical transmission path arranged on the printed board. Superior optical coupling is achieved between two points of the printed board and two points of the semiconductor part, thereby guaranteeing the arrangement of the semiconductor elements at the correct position.
Preferably, there is provided a printed board unit in which a semiconductor part including an optical device is packaged on a board and further photoelectric elements optically coupled to the semiconductor part are arranged on the board. Optical communication be performed between the printed board and the semiconductor part thereby guaranteeing the optical coupling between the two.
Preferably, there is provided a printed board unit in which a semiconductor part including an optical device is fixed by an adhesive on the board. The semiconductor part is fixed on the printed board without stress, and therefore the durability is improved.
Preferably, there is provided a positioning apparatus in which a position where an optical signal can be received with high sensitivity is automatically searched for while moving a semiconductor element for optically communicating with the printed board.
Preferably, the positioning apparatus includes a power terminal for supplying power to the optical device of the semiconductor part. A part dedicated to registration need not be arranged on the printed board, and a reduction in density of the wiring and the parts on the printed board can be prevented.
Preferably, the positioning apparatus is such that the adhesive for fixing the semiconductor part on the printed board is set upon completion of the positioning operation. The semiconductor part is automatically fixed on the printed board.
Preferably, the semiconductor part including an optical device is fixed on the printed board using an adhesive. In other words, the soldering is eliminated, thereby solving the problem that the semiconductor part is broken by the high-temperature heat generated by the soldering process.
Preferably, the semiconductor part mounted on the printed board and is moved while optically communicating with the printed board, thereby checking the receiving sensitivity. Relative positions of two mutually distant objects can be checked, and the correct position of a semiconductor part on the printed board can be found.